In a manufacturing line for, for example, semiconductor substrates or thin film substrates, inspection of defects present on the semiconductor substrate is performed to maintain and improve the production yield of the products. As conventional techniques, those described in Patent Publications 1 (Japanese Unexamined Patent Application Publication No. 09-304289) and 2 (Japanese Unexamined Patent Application Publication No. 2000-162141) are known. In order to detect a respective small defect, the inspection is performed in the manner that a laser beam focused to several tens of micrometers (μm) is irradiated onto to the surface of the sample, and light scattered from a defect is focused and detected.
In connection with the above-described method, a calculation is utilized method as described in Non-patent Publication 1 (P. A. Bobbert and J. Vlieger, “Light scattering by a sphere on a substrate”, Physica A, Volume 137, Issue 1-2, p. 209-242 (1986)). According to the technique, in a case where illumination light is irradiated on sphere particulates on a flat metallic dielectric member, the calculation method calculates the intensity and angular distribution of light scattered from the sphere particulates.
The technique for LSI wiring integration advances year by year, and the sizes of respective detection-target defects are now approaching a detection limit of optical inspection. According to the semiconductor road map, the defect detection capability is required to detect a defect having the size of 32.5 nm in 2007, and to detect a defect having the size of 20 nm or less in 2011 or subsequent years.
In order to achieve high speed inspection of a small defect, an amount of scattered light sufficient to enable the detector device to detect the defect has to be acquired from the defect. Hence, in order to achieve the inspection, it is effective to provide high-illuminance illumination by using a high power light source. However, when the illuminance is excessively increased, the amount of heat in the irradiated area is increased to the extent of damaging the LSI substrate. Hence, sensitivity improvement by increasing the illuminance is limited.
Further, in the case of an apparatus configuration arranged to be capable of detection of light scattered from a small defect, there occurs a large amount of light scattered from large-size or intermediate-size defects also present in the sample. Hence, the output power is saturated when those large or intermediate-size defects are detected by the same detector device used to detect the small defect. For example, the amount of light scattered from a particulate having a size of 500 nm is about 1,000,000 times as large as the amount of light scattered from a particulate having a size of 20 nm. Hence, in the event of detecting the latter light with use of a dynamic range (60 dB to 80 dB) of an ordinary photodetector device (such as a photoelectron multiplier tube or photodiode), a signal of the former light is saturated. When the output of the detector is saturated, a correct amount of scattered light is unknown, therefore making it difficult to achieve the calculation of the defect size in accordance with the amount of scattered light. Further, even in the case of identification of a defect position by use of, for example, the center of gravity of a defect waveform in accordance with a defect scatter signal, there is posed problems of, for example, deterioration in the accuracy of defect coordinate calculation due to saturation of the signal.